Electromagnetically actuated, single-surface friction coupling, without a rotor slip ring

ABSTRACT

The invention proposes an electromagnetically actuated, single-surface friction coupling without a rotor slip-ring, having a rotor element ( 2 ), a fixed magnet body ( 6 ) and a pot-shaped armature element ( 28 ) mounted so that it can be displaced axially. A cylindrical jacket shaped area ( 28 B) of the armature element ( 28 ) extends with a narrow air gap along an outer jacket surface ( 12 ) of the magnet body ( 6 ). Between the armature element ( 28 ) and a friction surface ( 30 ) of the rotor element there is a working air gap (S) that can be bridged. To keep the moment of inertia on the drive output side as small as possible, it is proposed to arrange the rotor element ( 2 ) on the drive output side and the armature element ( 28 ) on the drive input side.

FIELD OF THE INVENTION

The invention concerns an electromagnetically actuated, single-surfacefriction coupling without a rotor slip-ring, having a pot-shapedarmature element.

BACKGROUND OF THE INVENTION

An electromagnetically actuated friction coupling with an armatureelement of this type is shown in the not previously published documentDE 199 51 630. This coupling comprises a rotor element mounted so thatit can rotate, a fixed magnet body with a magnet coil, and a rotatablepot-like armature element which, however, is mounted so that it can bedisplaced axially. The armature element has a ring disc shaped area anda cylindrical jacket shaped area. With its cylindrical jacket shapedarea the armature element projects into an annular groove of the magnetbody in such manner that magnetic flux can be transferred via a narrow,radial air gap. Electromagnetically actuated couplings of thisstructural form can be manufactured inexpensively, take up littlestructural space, and are very reliable. A coupling of this type issuitable in hand-operated percussion drilling machines, for the couplingor release, as desired, of the drive motor from the drilling tool on thedrive output side. The coupling reacts to high loads and/or deflectionmovements of the housing of the percussion drilling machine, such asthose that occur when the drilling tool gets stuck. In this way, risk ofinjury to the machine operator can be avoided. The coupling described inDE 199 51 630 is designed such that when fitted in a percussion drillingmachine, the rotor element is in permanent drive connection with thedrive motor and the armature element is in permanent drive connectionwith the drilling tool or the drilling tool holder.

It has been shown that owing to the gear ratios on the drive outputside, when the coupling has been released and until the elements on thedrive output side have come to a complete stop, undesired reactiontorques can still act upon the housing of the percussion drillingmachine.

A further problem is that when the coupling has been released, althoughthe drive output side with the drilling tool comes to rest almost atonce, the drive input side of the coupling and the drive motor stillcontinue running for a few seconds even after the current supply to thedrive motor has been cut off, because of the stored rotation impulse.The machine is not ready for use again until the drive motor has come torest. Since as a rule it is desired to resume work with the drillingtool quickly after a coupling release process, this time taken for thedrive input side to come to rest is perceived as unacceptably long.

SUMMARY OF THE INVENTION

The purpose of the present invention is therefore to reduce to a minimumthe undesired reaction torques that can still occur after the couplinghas been released. The coupling should also be developed further in suchmanner that the time taken for the drive input side to come to restafter a coupling release process, is made shorter.

These objectives are achieved by an electromagnetically actuated,single-surface friction coupling without a rotor slip-ring, having thecharacteristics of the principal claim. According to this, the rotorelement is arranged on the drive output side and the armature element onthe drive input side. By virtue of its pot-like shape, associated withits cylindrical jacket surface the armature element has a considerablefraction of its total mass a large distance away from the centre ofrotation, and it therefore has a large moment of inertia. In contrast,the rotor element has a smaller diameter and a smaller proportion of itsmass far removed from the centre of rotation. Its moment of inertia istherefore very much lower, so that the rotation impulse that has to bedissipated on the drive output side once the coupling has been released,is very much smaller. ‘Snatching’ of a hand-operated tool after thecoupling release process is accordingly reduced to a minimum.

In an advantageous embodiment of the invention, the friction surface ofthe rotor element is associated with the side of the ring disc area ofthe armature element opposite the cylindrical jacket shaped area of thearmature element. In the engaged condition of the coupling the frictionsurface of the rotor element is in contact, so to speak, outside thepot-shaped armature on the bottom of the pot, such that the rotorelement is located substantially outside the axial structural spaceoccupied by the armature element. Accordingly, the rotor element is veryclose to the drive output side, which enables a short shaft withcorrespondingly low moment of inertia to be used on the drive outputside.

Corresponding to the larger moment of inertia on the drive input side ofthe coupling, after a coupling release process a higher rotation impulseremains in the system on the drive input side. To shorten the time takenfor the drive input side to come to rest after a coupling releaseprocess, in an advantageous embodiment of the invention the armatureelement can move axially between two end positions, in the first ofwhich it is frictionally engaged with the rotor element while in thesecond end position it is in frictional contact with a fixed brakingring.

This embodiment can advantageously be developed further in that thearmature element is or can be connected to an armature shaft by means ofan axially deflectable spring element, such that the armature element ispre-stressed against the braking ring by the spring element. In theabsence of current supply, as after a release of the coupling, thissimply constructed brake is actuated by the pre-stressing force of thespring element. Particularly in combination with an embodiment in whichthe friction surface of the rotor element is associated with the side ofthe ring disc shaped area of the armature element opposite thecylindrical jacket shaped area of the armature element, a coupling-brakecombination is provided by exceptionally simple means. The armatureelement then has a friction surface at each of its two axial ends. Onefriction surface is arranged on the ring disc shaped area of thearmature, so to speak on the bottom of the pot opposite the rotorelement, and one friction surface is arranged on the end of thecylindrical jacket shaped area opposite the braking ring. The frictionsurfaces of the rotor element and of the braking ring form axialabutments between which the armature element can move to and fro.

A design of the coupling which is favorable in terms of structural spaceis characterized in that a flange is provided on the armature shaft forconnection to the spring element, which supports the armature elementand which conducts a magnetic flux between the magnet body and the rotorelement when current is flowing through the magnet coil. If a first partof the flange extends with a narrow radial air gap axially along aninner jacket surface of the magnet body and a second part of the flangesurrounds a hub of the rotor element with a narrow radial air gap, themagnetic flux can be transferred with little loss, respectively acrossthe narrow radial air gaps between the components rotating at differentspeeds. Besides the function of mechanically coupling the armatureelement to the armature shaft on the drive input side, the flange alsofulfils the function of coupling the rotor element magnetically with themagnet body.

The electromagnetically actuated coupling according to the invention andits embodiments are suitable for coupling or releasing a drive motor anda drilling or percussion drilling tool in a hand-operated drilling orpercussion drilling machine, as desired, thanks to their small moment ofinertia on the drive output side, their compact structural form andtheir low manufacturing cost.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

The only FIGURE shows a rotor element arranged on a rotor shaft.

DETAILED DESCRIPTION OF THE INVENTION

In the only FIGURE shown, a rotor element 2 is arranged on a rotor shaft4. The rotor shaft 4 is mounted and able to rotate by virtue of bearings(not shown). A fixed magnet body 6 is provided with a magnet coil 8,said coil being arranged between an inner jacket surface 10 and an outerjacket surface 12 of the magnet body. The magnet body 6 is arranged in afixed position in the housing 14 of the coupling, so that current can besupplied to the magnet coil 8 without the use of slip-rings. Aball-bearing 16 is held, in the inner jacket 10 of the magnet body 6, bya retaining ring 18 seated on an armature shaft 20 on the drive inputside. An axially springy but rotationally rigid spring element 26 isattached to a flange 22, rotationally fixed with respect to the armatureshaft 20, by means of fixing screws 24. A possible design of the springelement is described in the aforementioned DE 199 51 630. It is to beunderstood that the content of that earlier application is incorporatedinto the disclosure content of the present application.

The spring element 26 supports the armature element 28, which istherefore connected with the flange 22 in a rotationally rigid way butwhich can be displaced axially relative to the flange. The armatureelement 28 is pot shaped with a ring disc shaped area 28A and acylindrical jacket shaped area 28B. Between the cylindrical jacketshaped area 28B of the armature element and the outer jacket surface 12of the magnet body 6 there is a narrow radial air gap, across which amagnetic flux can be transferred from the armature element to the magnetbody or vice-versa. Between the ring disc shaped area 28A of thearmature element and an axially opposed, ring disc shaped frictionsurface 30 of the rotor element 2 there is an axial, working air gap Swhich can be bridged. When electric current flows through the magnetcoil 8, magnetic poles are formed in the area of the working air gap Son the rotor element and on the armature element, between which there isa force of attraction. Due to this force of attraction, the armatureelement 28 is displaced axially towards the rotor element so that theworking air gap S is bridged and the two elements come into frictionalengagement with one another.

This is the switching position adopted by the coupling in ahand-operated drilling or percussion drilling machine during operation.The drilling or percussion drilling machine is then driven by a drivemotor. If an overload occurs or if a deflection movement of the housingof the machine larger than a predetermined size is detected, then thetool on the drive output side of the drive motor is uncoupled from thelatter, since the magnet coil 8 is, in such a case, switched off. Thepre-stressing force of the spring element 26 then separates the armatureelement 28 from the rotor element.

The drive output side of the coupling, which is formed of the rotorelement 2 and the rotor shaft 4, has only a very small moment of inertiaand because of this any further displacement movement after the releaseof the coupling is reduced to a minimum.

The friction surface 30 of the rotor element 2, shown in FIG. 1, isassociated with the side of the ring disc shaped area 28A of thearmature element 28 opposite the cylindrical jacket shaped area 28B ofthe armature element 28. The axial movement of the armature element 28is restricted, on one side, by the rotor element 2 and, on the otherside, by a braking ring 32. The armature element 28 can move axiallybetween two end positions, in the first of which, on the left, it isfrictionally coupled with the rotor element 2 while in the second endposition on the right, it is in frictional contact with the fixedbraking ring 32. When there is no current in the coupling, the springelement 26 exerts an axial pre-stressing force on the armature element28 which presses the armature element axially against the braking ring.When the coupling has been released, the armature shaft 20 with thearmature element 28 and the drive motor, coupled thereto in a drivingconnection, is braked to rest in a short time. Accordingly, for themachine operator the waiting time until the machine is again ready foroperation, after a coupling release process, is very short.

The flange 22, which provides the driving connection between thearmature shaft 20 and the spring element 26 and the armature element 28,extends with a narrow radial air gap along part of the inner jacketsurface 10 of the magnet body 6. A magnetic flux is transferred acrossthis narrow radial air gap from the magnet body to the flange. In asecond area of the flange, a hub 34 of the rotor element 2 is enclosedwith a narrow radial air gap. A magnetic flux, represented by the line36 and established when current flows through the magnet coil 8,therefore flows from the radially inner jacket surface 10 of the magnetbody 6 across an air gap to the flange 22, from there across a narrowradial air gap to the hub 34 of the rotor element, from there across thebridged working air gap S to the pot shaped armature element 28, andfrom there across a narrow radial air gap to the outer jacket surface 12of the magnet body 6.

List of index numbers  2 Rotor element  4 Rotor shaft  6 Magnet body  8Magnet coil 10 Inner jacket surface 12 Outer jacket surface 14 Housing16 Bearing 18 Retaining ring 20 Armature shaft 22 Flange 24 Screw 26Spring element 28 Armature element 28A Ring disc shaped area 28BCylindrical jacket shaped area 30 Friction surface 32 Braking ring 34Hub 36 Magnetic flux

What is claimed is:
 1. An electromagnetically actuated, single-surface friction coupling without a rotor slip-ring, the friction coupling comprising: a rotor element (2) mounted so that the rotor element (2) can rotate; a fixed magnet body (6) provided with a magnet coil (8) and an armature element (28) which can rotate but is mounted so that it can be axially displaced, the armature element (28) being pot shaped with a ring disc shaped are (28A) and a cylindrical jacket shaped area (28B), such that the cylindrical jacket shaped area (28B) of the armature element extends with a narrow air gap axially along an outer jacket surface (12) of the magnet body; and an axial working air gap (S), between the ring disc shaped area (28A) of the armature element and an axially opposed, ring disc shaped friction surface (30) of the rotor element (2), which can be bridged, the armature element (28) being able to be displaced axially by a magnetic force and brought into frictional engagement with the rotor element (2), and the rotor element (2) is arranged on the drive output side and the armature element (28) is arranged on the drive input side.
 2. The friction coupling according to claim 1, wherein the friction surface (30) of the rotor element is associated with a side of the armature element (28) corresponding to its ring disc shaped area (28A), which is opposite the cylindrical jacket shaped area (28B) of the armature element (28).
 3. The friction coupling according to claim 2, wherein the armature element (28) is axially movable between two end positions, such that in a first end position the armature element (28) is coupled in frictional engagement with the rotor element (2) and in a second end position, the armature element (28) is in frictional contact with a fixed braking ring (32).
 4. The friction coupling according to claim 3, wherein the armature element (28) is connected to an armature shaft (20) via an axially deflectable spring element (26) and the armature element (28) is axially pre-stressed by the spring element (26) against the braking ring (32).
 5. The friction coupling according to claim 4, wherein a flange is provided on the armature shaft (20) for connection with the spring element (26), and the flange transfers magnetic flux (36) between the magnet body (6) and the rotor element when current is flowing in the magnet coil (8).
 6. The friction coupling according to claim 5, wherein a first part of the flange extends with a narrow radial air gap long an inner jacket surface (10) of the magnet body (6) and a second part of the flange surrounds a hub (34) of the rotor element with a narrow radial air gap.
 7. The friction coupling according to claim 1, wherein the friction coupling is incorporated within a hand-operated drilling machine.
 8. The friction coupling according to claim 1, wherein the friction coupling is incorporated within a percussion drilling machine.
 9. A drilling machine having an electromagnetically actuated, single-surface friction coupling without a rotor slip-ring, the friction coupling comprising: a rotor element (2) mounted so that the rotor element (2) an rotate; a fixed magnet body (6) provided with a magnet coil (8) and an armature element (28) which can rotate but is mounted so that it can be axially displaced, the armature element (28) being pot shaped with a ring disc shaped are (28A) and a cylindrical jacket shaped area (28B), such that the cylindrical jacket shaped area (288) of the armature element extends with a narrow air gap axially along a outer jacket surface (12) of the magnet body; and an axial working air gap (5), between the ring disc shaped area (28A) of the armature element and an axially opposed, ring disc shaped friction surface (30) of the rotor element (2), which can be bridged, the armature element (28) being able to be displaced axially by a magnetic force and brought into frictional engagement with the rotor element (2), and the rotor element (2) is arranged on the drive output side and the armature element (28) is arranged on the drive input side.
 10. The drilling machine according to claim 9, wherein the drilling machine is a hand-operated drilling machine.
 11. The drilling machine according to claim 9, wherein the drilling machine is a percussion drilling machine.
 12. An electromagnetically actuated, single-surface friction coupling without a rotor slip-ring, the friction coupling comprising: a rotor element (2) mounted so that the rotor element (2) can rotate; a fixed magnet body (6) provided with a magnet coil (8) and an armature element (28) which can rotate but is mounted on a drive input so that it can be axially displaced relative to the drive input and the drive output, the armature element (28) being pot shaped with a ring disc shaped area (28A) and a cylindrical jacket shaped area (28B), such that the cylindrical jacket shaped area (28B) of the armature element extends with a narrow air gap axially along an outer jacket surface (12) of the magnet body; and an axial working air gap (5), between the ring disc shape area (28A) of the armature element and an axially opposed, ring disc shaped friction surface (30) of the rotor element (2), which can be bridged, the armature element (28) being able to be displaced axially by a magnetic force and brought into frictional engagement with the rotor element (2), and the rotor element (2) is arranged on a drive output and the armature element (28) is arranged on the drive input. 